Non-ideal absorption effects on hydrogen permeation through palladium–silver alloy membranes

McLeod, Logan S.; Degertekin, F. Levent; Fedorov, Andrei G.

doi:10.1016/j.memsci.2009.04.036

Cited by 13 publications

(7 citation statements)

References 31 publications

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“…In a diffusion-limited regime, the apparent activation energy for permeation consists of a contribution from the heat of Catalysis Science & Technology Paper adsorption (exothermic) and activation energy for diffusion (endothermic). 25 For Pd, the activation energy for diffusion outweighs the heat of H 2 adsorption, resulting in a positive apparent activation energy for permeation. 17,26 As illustrated in Fig.…”

Section: Hydrogen Permeation Characteristicsmentioning

confidence: 99%

Improved benzene production from methane dehydroaromatization over Mo/HZSM-5 catalysts via hydrogen-permselective palladium membrane reactors

Natesakhawat

Means

Howard

et al. 2015

Catal. Sci. Technol.

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The effectiveness of hydrogen-permselective palladium membrane reactors for non-oxidative methane dehydroaromatization (MDA) over 4 wt% Mo/HZSM-5 catalysts was investigated as a function of weight hourly space velocity (WHSV) at 700 °C and atmospheric pressure. CH4 conversion and aromatic product yield decrease with increasing WHSV from 750 to 9000 cm 3 gcat -1 h -1 . C6H6 is the main C-containing product at and below 3000 cm 3 gcat -1 h -1 whereas C2H4 dominates the C-product distribution at higher WHSVs. Due to selective removal of H2 from the reaction products in catalytic membrane reactors, C6H6 yield is significantly improved over the whole WHSV range compared to those obtained in fixed-bed reactors. H2 recovery is strongly influenced by WHSV as it decreases from 48.3% at 750 cm 3 gcat -1 h -1 to 6.8% at 9000 cm 3 gcat -1 h -1 . There exists a trade-off between catalytic activity and H2 recovery, which results in the maximum enhancement (~360%) in C6H6 yield at 3000 cm 3 gcat -1 h -1 . At this intermediate space velocity, the largest concentration of H2 is found in the retentate stream and helps alleviate coke accumulation particularly on HZSM-5. Carbon is deposited on the inner surface of the membrane reactor portion in contact with the catalyst bed and transports to the outer surface, thus causing H2 permeability to decrease over the 15-h reaction period.Palladium membrane reactors significantly improve C 6 H 6 yield from CH 4 dehydroaromatization on Mo/HZSM-5 catalysts over a wide range of space velocity.

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Section: Hydrogen Permeation Characteristicsmentioning

confidence: 99%

Improved benzene production from methane dehydroaromatization over Mo/HZSM-5 catalysts via hydrogen-permselective palladium membrane reactors

Natesakhawat

Means

Howard

et al. 2015

Catal. Sci. Technol.

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“…For example, alloying palladium with silver results in alloys that, in several ways, are superior to pure palladium, particularly as hydrogen purification materials. Like pure palladium, palladium-silver alloys are virtually 100% selective to the absorption of hydrogen from a gas mixture [10][11][12][13][14]. Palladium-silver alloys have been found to have superior hydrogen transport properties and some resistance to hydrogen embrittlement, as compared to pure palladium [10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…Like pure palladium, palladium-silver alloys are virtually 100% selective to the absorption of hydrogen from a gas mixture [10][11][12][13][14]. Palladium-silver alloys have been found to have superior hydrogen transport properties and some resistance to hydrogen embrittlement, as compared to pure palladium [10][11][12][13][14]. With respect to the resistance of palladium-silver alloys to hydrogen embrittlement, most studies done in this area have been qualitative or, at best, limited in their quantitative characterization.…”

Section: Introductionmentioning

confidence: 99%

Strength, Hardness, and Ductility Evidence of Solid Solution Strengthening and Limited Hydrogen Embrittlement in the Alloy System Palladium-Copper (Cu wt. % 5–25)

et al. 2021

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Strength, hardness, and ductility characteristics were determined for a series of palladium-copper alloys that compositionally vary from 5 to 25 weight percent copper. Alloy specimens subjected to vacuum annealing showed clear evidence of solid solution strengthening. These specimens showed, as a function of increasing copper content, increased yield strength, ultimate strength, and Vickers microhardness, while their ductility was little affected by compositional differences. Annealed alloy specimens subsequently subjected to exposure to hydrogen at 323 K and PH2 = 1 atm showed evidence of hydrogen embrittlement up to a composition of ~15 wt. % Cu. The magnitude of the hydrogen embrittlement decreased with increasing copper content in the alloy.

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“…Morreale et al commented that their p H 2 exponent of n = 0.62 was due either to “an invalid assumption of a diffusion-limited mechanism and/or to changes in the Sieverts’ constant and diffusion coefficient with increasing pressure”, i.e., both possibilities were proposed for the deviation from 0.5. Very recently, McLeod et al analyzed nonideal effects on H permeation through a Pd 0.75 Ag 0.25 alloy membrane as being due to deviations of the solubilities from ideal behavior using data from the literature; , however, they neglected the influence of the nonideality on the diffusion constant.…”

Section: Introductionmentioning

confidence: 99%

Exponents for the Pressure Dependence of Hydrogen Permeation through Pd and Pd−Ag Alloy Membranes

Flanagan

Wang

2010

J. Phys. Chem. C

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A frequently employed boundary condition for H permeation of membranes is p down ≈ 0 and, for this case, the flux is given by J = (KD H/d)p up n , where K is a constant and d is the membrane thickness. Values of n can then be obtained from slopes of plots of ln J against ln p up. When the H solution is ideal, n = 0.5, and D H is concentration-independent, but when the H solution is nonideal, i.e., when the H atoms interact, n ≠ 0.5 and D H is concentration-dependent. An equation is derived for n, which includes the effects of nonideality of H on both D H and the solubility. The terms in this equation for n can be obtained from the appropriate equilibrium H2 isotherms for Pd or its alloys. Good agreement is found between the derived values of n and the experimental values for the pressure dependence of H2 permeation through Pd, Pd0.77Ag0.23, and Pd0.50Ag0.50 membranes. By comparing experimental n ≠ 0.50 values to those calculated from the equilibrium isotherms, a decision can be made about whether bulk diffusion is the slow step.

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Non-ideal absorption effects on hydrogen permeation through palladium–silver alloy membranes

Cited by 13 publications

References 31 publications

Improved benzene production from methane dehydroaromatization over Mo/HZSM-5 catalysts via hydrogen-permselective palladium membrane reactors

Improved benzene production from methane dehydroaromatization over Mo/HZSM-5 catalysts via hydrogen-permselective palladium membrane reactors

Strength, Hardness, and Ductility Evidence of Solid Solution Strengthening and Limited Hydrogen Embrittlement in the Alloy System Palladium-Copper (Cu wt. % 5–25)

Exponents for the Pressure Dependence of Hydrogen Permeation through Pd and Pd−Ag Alloy Membranes

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